Cyclometalated IrIII Complex Possessing Chiral MIC ligand: Regiospecific sp3 C-H Activation and Asymmetric Transfer Hydrogenation of Ketone.

Abstract

Cyclometalation offers a wide number of organometallic metallacycles showing diverse applications. However, such NHC complexes synthesized via an sp³ C-H bond activation are rare. An iridium(III) complex with a chiral mesoionic N-heterocyclic carbene (MIC) ligand, where the Ir^III forms an additional Ir-C bond via a regiospecific sp³ C-H bond activation at the N-methylbenzyl wingtip, was synthesized and characterized. To our best knowledge, this represents the first example of cyclometalated iridium(III) complex possessing a chiral MIC donor ligand. The formation of the complex was followed by 2D correlation NMR spectroscopy and the molecular formula mass was evidenced by ESI-HRMS mass spectrometry. The molecular structure of the Ir^III-MIC complex was unambiguously established by the single crystal XRD data. This cyclometalated Ir^III complex was employed in the asymmetric transfer hydrogenation of 4-bromoacetophenone, and the complex was successful to transfer chirality to the final alcohol molecules (up to 92 % ee).